The present invention relates to thermoelectric temperature control systems and is directed more particularly to an improved thermoelectric temperature control assembly which is specially adapted for use in centrifuges.
Because of their small size and weight, thermoelectric devices which utilize the Peltier effect have come into widespread use as solid-state heating and cooling elements. Thermoelectric devices have, for example, been widely used to control the temperatures of vessels and compartments, such as the refrigerated rotor compartments of centrifuges. One reason for this widespread use is that thermoelectric devices do not exhibit the high thermal mass that characterizes temperature control systems which utilize liquid baths. This, in turn, allows the temperature that is established by the system to be changed at a rapid rate, thereby greatly increasing the rate at which batches of samples may be processed. Another reason for this widespread use is that the direction of heat flow through a thermoelectric device can be reversed by simply reversing the direction of current flow therethrough. As a result, temperature control systems which utilize thermoelectric devices need not utilize separate heating and cooling elements.
One important consideration in the design of thermoelectric heating and cooling systems is the provision of structures whereby the heat which is removed or supplied by its thermoelectric devices may be conducted away from or toward the outer surfaces thereof. In some thermoelectric heating and cooling systems, for example, the outer surfaces of the thermoelectric devices are connected to a heat sink over which air is circulated. In other thermoelectric heating and cooling systems, the outer surfaces of the thermoelectric devices are connected to jackets through which water is circulated. A system of the latter type which is used to cool a centrifuge is shown in U.S. Pat. No. 3,347,453, which issued on Oct. 17, 1967 in the name of K. Goergen.
Another important consideration in the design of thermoelectric heating and cooling systems is the maintenance of a low thermal resistance between the inner and outer surfaces of the thermoelectric devices and the structures with which those surfaces are in contact. This low thermal resistance may, for example, be established, in part, by grinding the contact surfaces flat and smooth and by applying thermally conductive grease therebetween. The desired low thermal resistance may also be established by using clamping arrangements to create a relatively high contact pressure between the thermoelectric devices and the structures with which they are in contact.
Prior to the present invention, the clamping arrangements that have been used with thermoelectric devices have been relatively bulky and complex. Some clamping arrangements, for example, have required that each thermoelectric device be surrounded by a plurliaty of symmetrically positioned bolts which squeeze each device between the item to be cooled and a heat sink. Because each of these clamping bolts provides a thermal leakage path across the respective thermoelectric device, however, such arrangements have a poor efficienty.
Other clamping arrangements have required the use of a plurality of bolt-tightened clamps for clamping each edge of each thermoelectric device to the desired contact surface. When several thermoelectric devices are used with a clamping arrangement of this type, however, much time and effort is consumed in properly positioning and tightening the many separate pieces. The cost of assembling a thermoelectric heating and cooling system of this type is further increased by the fact that provision must be made for routing and securing the leads of each thermoelectric device. Thus, clamping arrangements of this type are costly and time consuming to install.